Conversion of sodium sulfide to sodium sulfite



Jan. 12, 1965 I J. E. GREENAWALT 3,165,373

CONVERSION OF SODIUM SULFIDE T0 SODIUM SULFITE Filed June 26. 1961 2Shasta-Sheet 1 Jan. 12, 1965 J. E. GREENAWALT 3,165,378

CONVERSION OF SODIUM SULFIDE TO SODIUM SULFITE Filed June 26. 1961 2Sheets-Sheet 2 26 2+ l I 2| v 25 2| United States Patent 3,165,378CONVERSION OF SQDIUM SULFIDE T0 SGDHJM SULFITE John Eckert Greenawait,Bronxville, N.Y.; Joy S. Greenawait, executrix of said John E.Greenawait, deceased Filed June 26, 1961, Ser. No. 119,445

7 Claims. (Cl. 23129) the particular digester or cooking process that isused for freeing the cellulose fibers from encrusting matter. Forexample, a solution of caustic soda and sodium sulfide is used as theactive chemicals in the sulfate or kraft'process; caustic soda is usedin the soda process; and in the sulfite process, an acid sulfitesolution, sometimes referred to as bisulfite of lime liquor is used.Sodium sulfite also is used. In all these processes the problem is todissolve and remove the resinous or encrusting matter to free thecellulose fibers contained in wood, or rags, or straw, etc., used forthe production of paper. The dissolving agents most commonly used arevery active and they act not only upon the encrusting and non-celluloseconstituents but also to a greater or lesser extent upon the pulp-makingfibers themselves and may destroy or injure a considerable portion ofthe valuable fibers which are intended to be used for the production ofpaper. The yield with the various more active chemicals varies with thecharacter of the wood treatedand is usually from 38% to 55% of the dryweight of the wood treated. By the use of substantially neutral sodiumsulfite solution which is considered to be a milder acting chemical, theyield of desirable fibers may be increased 25% to due to the mildersolvent action of the solvent. Sodium sulfite (Na SO is used as theactive chemical in a dilute solution of approximately 12% in thesemi-chemical process; but to realize the full benefits of the use ofsodium sulfite cooking liquor it is desirable to use a 30% to solution.

Such a highly concentrated solution is uneconomical and impractical touse without a successful and economirecovery and regenerating processwhich will permit the use and-reuse of the sodium sulfite for cookingthe wood in the digesters. I

. It is an object of this invention to provide such a process by whichto recover the spent sodium sulfite liquor and regenerate the chemicalstherein to the initial sodium sulfite form so that the chemical may beused again, then recovered,-.regenerated, and reused repeatedly. To'accomplish this desirable end the invention, in one way of stating it,provides a method for converting sodium sulfide (Na s) to sodium sulfite(Na SO In further explanation of the foregoing statement, it ismentioned here that the spent liquor, from the wood digesters in thechemical process of producing pulp, contains carbonaceous and ligneousmatter in addition to the spent chemicals. Processes are known forseparating the carbonaceous and ligneous matter contained in the spentliquor from the chemicals, by burning or otherwise. Some of theseprocesses produce a smelt in which. the chemical is in the form ofsodium sulfide. Or sodium sulfide may be produced by smelting sodiumsulfate (salt cake) in a reducing atmosphere. Or it may be provided fromother sources. While the process of conversion of sodium sulfide tosodium sulfite according to the invention is applicable whether thesodium sulfide is produced from black liquor which comes from pulpdigesters or whether it comes from other sources, the invention isparticularlysuited to the recovery of chemicals and regeneration of thechemicals in pulp-producing processes employing sodium sulfite in thecooking liquor.

According to the process of this invention, sodium sulfite is oxidizedin an atmosphere of saturated steam and oxidizing gases, such as air oroxygen containing gases under controlled pressure materially greaterthan atmospheric and under controlled conditions of temperature. Theconversion is believed to be accomplished by direct oxidation of thesodium sulfide according to the following reaction: 7

It is important in my process that the temperature be carefullycontrolled within a narrow range and preferably at a constanttemperature, in the zone where the oxidation reaction takes place. Ifthe temperature is permitted to go too high, the oxidation of the sodiumsulfide proceeds to the-formation of unwanted sulfate, and this reactionis believed to proceed as follows:

But this unwanted oxidation may be practically substantially avoided bynot permitting the temperature in the reaction zone to rise above 350 F,provided the reaction is carried out in the presence of saturated steam.However, the temperature should not be permitted to go below 310 F.because the desired oxidation of the sulfide to sulfite will not thenproceed in satisfactory manner. I have obtained satisfactory resultswhen the temperature in the reaction zone was maintained between 310" F.and 350 F. Not only is it important in my process to control andmaintain the temperature within a limited range but it is imporant thatthe zone in which the oxidation reaction takes place be maintained at apressure substantially greater than atmospheric. In my process thepressure in the reaction zone, wherein are present the saturated steam,air (or oxygen) and the solution containing the reacting sulfurcompounds, should be within the range of eighty to one hundredtwenty-five pounds per square inch (gauge), and preferably about onehundred twenty-five, although in some instances a pressure as low assixty pounds may sufiice.

If the source of the sodium sulfide is the concentrated or smeltedproduct from black liquor or if it otherwise comes from spent liquor inapulp digesting or paper making process other sulfur compounds such as,sodium thiosulfate, or caustic soda or both, may be present in thecharge in small amounts or formed during the course of the process. Butthis is not a serious drawback in my process for the thiosulfate and thecaustic soda will react to form sodium sulfite according to thefollowing:

tion of pulp, is concentrated. The spent liquor, containing the spentsulfite chemicals and the dissolved resinous and ligneous matter, isevaporated in a known way to contain about fifty percent, or more, ofsolids. This concentrated liquor is then burned in a known way in asmelting furnace under reducing conditions so as to convert the sulfurcompounds into sodium sulfideform. The sodium sulfide smelt isdischarged from the smelting furnace as amolten stream and this maycontain other sulfur compounds, such as thiosulfate in small amount'andcaustic soda along with sodium sulfide. The smelt is then dissolved inwater and this solution constitutes the charge or solution which is thentreated according to my process for conversion of the sodium sulfide tosodium sulfite suitable for reuse as a cooking liquor in the wood pulpdigesters. if sodium carbonate is present in the liquor, the smelt willcontain sodium carbonate. t

The following analysesof solutions, for example, show results obtainedbymy process operated at .80 pounds steam pressure; there being acertainaniount of concentration of'the solutions due to the drivingotfof some steam duringthe treatment.

In the regenerated solution the important thing is the conversion of thesodium sulfide to sodium sulfite. The thiosulfate may be useful in thecooking operation but preferably should be kept at a minimum as a largeamount has ,a tendency to darken the color of the pulpv being treated.The small amount of sodium sulfate is not harmful as it is inactiveduring the cooking process and will be converted to sodium sulfide inthe furnace operation during a succeeding cycle. Sodium carbonate ispreferred in some operations and aids in maintaining the alkalinity ofthe solution. 7

Although the process of my invention may becarried out in'variousformsof apparatus, I have shown in the drawings, for illustrative purposes,one form of apparatus in which the process of my, invention may bepracticed. And although the novel features which are believed to becharacteristic of my invention are pointed out ,in the c, d, e, f, g,It, i, j, k, l, in, 21, 0, 17, q, r, s, t connected inseries by nipples15a to s inclusive. This serpentine conduit made by connecting theelbowsin series constitutes in efiect a reaction chamber 1%) defining areaction zone ltd, andproviding a meandering course or path of travelfor the charge solution, as describedlater on.- The serpentine chamberill provided by the elbows is mounted vertically'within a housing orcasing 15, which, as shown, is a suitable length of-twenty-four inchsteel pipe. The lower end of the casing 16 has welded thereto an annularflange It: and'the upper end has a corresponding flange The casing 16 isclosed at both ends; by a blind flange 9. at it'slower end, and a blindflange 2% at its upper end." It will be observed that the upper casingflange Edissuitably secured't'o the closure-flangem and the lower casingflange 17 .to the closure flange 19; which may be by bolts 21. The lowerclosure flange 1") has a downwardly extending hollow boss 22 throughwhich extends an outlet nipple ZSconnectedtO elbow 14a. The 'upperclosure flange hasa corresponding upwardly extending hollow. bossZFrthrough which extends an'inlet nipple 2-4 connected to elbow Mt.Nipples 23 1 and 24- are mounted in the. hollow bosses and suitablysealed on their exteriors by packing materialzlfi in a manner thatprovides top closureZil. This pipe 26 has a valve Zea and'is annexedclaims, the invention itself as to its objects and advantages and themanner in which it may be carried out may be better understood byreference to thefollowing more detailed description taken in connectionwith the accompanying drawings forming a part hereof, in which: FIG. 1is a view in elevation partly in section,'partly broken away, andlargely diagrammatic, showing one form of apparatus for carrying out themethod of my invention;

FIG. 2 is a view in elevation partly in section and largely diagrammaticof the reaction chamber or tower and to. larger scale;

FIG. 3 is a plan view of the reaction tower shown in FIG. 2.

Referring now to the drawings in which like reference charactersindicate like parts-throughout the several views, the apparatus as showncomprises a reaction chamber 10, a pro-heater 11, a receiver tank 12 anda cooling and settling chamber 13. r The reaction zone 14, as shown, is

. provided by mounting a series of six inch elbows 14a, b,

connected toa suitable source of steam (not shown) preferably undersufficient pressure tornaintain, if desired, a pressure higher than 8poundsv per squareinch gauge within the housing chamber127. The bottomclosure 19 is provided with an outlet pipe ZS-With' valve 28a forwithdrawing condensed water that may be formed in chamber 27. The steamline 26 may be: connected with appropriate valves to the same steamsupply line as the reaction zone so the pressure-will always be thesame.

The preheater. ill, aslshown, comp-rises a casing 31 closed at both endsby closure members 32, 33. Mounted within the casing 31 is a pipeconduit' 34 made up ofsuitable lengths of 'pipesfifi connected in seriesby=return bends 36. The inlet end of preheater conduit 34 is connectedto a T 37 towhich is connected an air inlet pipe 38 for introducing airand a raw'solution pipe 39 for introducting the. charge solution. Theraw or charge solu.tion, as explained later, is an aqueous solutioncontaining sodium sulfide which it is desired to convert to sodiumsulfite and,as described hereiis the sodium sulfide smelt describedhereinbefore .Which I has been recovered from the burning of blackliquor in a reducing atmosphere; However, itjwill bef-understood thatthe methodis applicable to any of the alkali metal sulfides whichrnay beconverted intothe corresponding sulfite.

A stearn'pipe 49, connected to a suitable sourceof steam leads into thepreheater housing 31 and an outlet steam pipe 41' having a regulatingvalve-42h connected to the opposite end of thepreheater housing. Asindi-- placed a pressure regulatin valve 26. A pressure gauge 47 in line45 serves to indicate the pressure within the reaction Zone 14. Apressure gauge 61 connected to' housing chamber 16 serves to'indicatethe" steam pressure in the housing. I i

The discharge conduit 45 leads into a treated solutionreceiving tank 12,havinga draw-off pipe tdiand valve 49 for drawing off treated-solution.The receiving tank E2 has connected thereto at'its upper sidea vapor anddrain-back conduit 5%, which leads in'to the bottom of a cooling andsettling chamber 13 which, as shown, isa with the upper end 3,1 east/ slength of large size pipe 51 closed at its upper end by a closure 52 andat its base end by a closure 53. The cooling chamber 51 is mounted on asuitable foundation and base 62. Mounted within the cooling chamberhousing 51 is a cooling coil 54 having an inlet 55 connected to asuitable source of cooling water (not shown) and an outlet 56. Thecooling chamber 13 is provided at its upper end with a vent pipe 57 fordischarge to atmosphere of residual gases and uncondensed vapors. Thevent pipe 57 is provided with a blow o or pressure regulator valve 57a,which may be set to maintain any desired pressure within the chamber 13so as to maintain, in turn, the desired pressure and temperature withinthe reaction zone 14. By maintaining the pressure the same as the restof the equipment the efficiency may be enhanced.

The process and apparatus may be operated as follows: Raw solution isintroduced through pipe 39 into preheater coil 34 together withcompressed air which is introduced from a suitable source, through pipe38. The raw solution is an aqueous solution of sodium sulfide from asuitable source. The amount of air introduced is sufficient to providean excess of oxygen necessary to convert the sulfide to sulfite. Thisraw solution, for example, may be an equeous solution made up from thesodium sulfide smelt resulting from the burning of concentrated spentblack liquor from the pulp digesters in which sodium sulfite solutionhas been used for cooking the wood chips.

As the mixture of air and raw solution (this mixture is herein calledthe charge mixture) passes through the preheater coil 34 in thepreheater 11, it is heated by steam introduced into the housing 31through'pipe 40. It will be understood, of course, that the chargemixture is introduced under sufficient pressure to pass through thesystem. Suflicient heat is applied in the preheater to bring thetemperature of the charge of raw solution and air as it enters the upperend of the reaction chamber to the neighborhood of the temperature atwhich the reaction zone is maintained. A suitable temperature forintroducing the charge solution into the reaction zone is in theneighborhood of 300 F. This temperature may go even as high as 350 F.,but inasmuch as it is desired to maintain the temperature Within thereaction zone 14 within the range of 310 to 350 F., and the reaction tooxidize the sulfide to sulfite is an exothermic reaction, thetemperature of the charge mixture entering the reaction zone should bemaintained so that the temperature in the reaction zone is maintainedwithin the desired range. This may be done by regulating the pressure inthe reaction zone. The temperature in the preheater coil, as will beseen, may be adjusted by adjusting the steam introduced in the preheaterand according to the temperature and amount of solution and airintroduced into the preheater. It is desirable, but not necessary,tohave the temperature of the solution being treated as it leaves thepreheater the same as the temperature in the reacting zone as theefiiciency of the reacting zone is thereby increased. The concentrationof the sodium sulfide in the raw solution may vary but preferably shouldbe such that the concentration of sodium sulfite in the treated solutionreceived in the receiving tank 12 would be suitable as a sodium sulfitecooking liquor. But even this may vary and the treated solution may beadjusted for use in the paper-making process.

The charge moves downwardly in the serpentine reaction chamber 10 in thepresence of the oxidizing air and saturated steam and it will be notedthat the reaction chamber is filled with steel balls ilwhich providemore surface area over which the solution is spread as it descends, thusthe stream of liquor being treated is broken up into very thin layersand each ball is completely covered with film so that morev surface filmof solution is exposed for reaction with the oxygen of the airintroduced with the charge. As the liquid charge descends it is causedto follow a tortuous path as the elbows cause turns in direction of flowand a mild turbulence to insure intimate contact between the chemicalreagents dissolved in the solution and the reactive oxygen or otherreacting agents intermediately formed as the reaction proceeds. Asmentioned hereinbefore, the temperature in the reaction zone ispreferably maintained within the range of 310 F. to 350 F.

It is a feature of my process that the pressure at which the reaction iscarried out be maintained substantially higher than atmospheric andpreferably under at least four atmospheres. The temperature in reactionchamber is positively controlled by the pressure of the steam with itsoxidizing gases and the boiling point of the solution being treated,which depends upon its density or specific gravity since the boilingpoint will be higher, the greater density of the solution. However, withthe same solution continuously flowing through the system, as is thecase in this instance, the temperature may be maintained constant bymaintaining a constant pressure in the system, notwithstanding that heatis released by the oxidation of the chemicals in the solution. Theutilization of this principle is highly important to the success of myprocess because if there should be an increase in temperature in thereaction zone which would be conducive to the formation of unwantedcompounds, such, for example, as sodium sulfate, the excess heat isimmediately dissipated for the reason that the increase in pressurebrought about by increase in temperature is immediately released withconcomitant using up of the excess heat as latent heat of vaporization.Hence, in my process the desired temperature of reaction is maintainedconstant. That is, if at a given increase in temperature, the oxidationof sodium sulfide (Na s) will proceed beyond the sulfite (Na SO and thecompound take up another atom of oxygen and form unwanted sodium sulfatem son, this unwanted increase in temperature is easily and readilyavoided by my process.

At the temperature at which the reaction zone is maintained, that is, ata temperature within the range of 310 F. to 350 F., some of the water inthe charge is converted into steam. That is, the condition of thesolution in the reaction chamber is such that saturated steam and liquidwater prevails under the pressure maintained which preferably is withinthe range of 80 to 125 pounds per square inch gauge pressure. in orderto maintain this desired pressure constant, the pressure regulator valve46 may be set accordingly, so that if the pressure within the reactionzone exceeds a predetermined amount (say 80 p.s.i., for example) theregulator valve'46 will automatically release the excess and maintainthe reaction zone pressure constant. Or, the pressure in the system maybe controlled by adjusting the blow oft pressure of valve 57a in thevent pipe 57; the important consideration being to control thetemperature in the reaction zone. This type of regulation has a furtheradvantage in that for any given pressure within the reaction zone(indicated on gauge 47) the saturated steam in the reaction zone willhave a fixed temperature, thus the arrangement provides a simple andeffective way of controlling both pressure and temperature within thereaction zone.

I prefer to mount the reaction chamber 14 within a housing 16 equippedwith a steam inlet such as inlet 25, and a steam outlet, such as steamoutlet 23. If desired, the valve 28;; may be of the blow off type. Thishas the advantage of providing positive temperature control in thehousing 16. The housing chamber 16 is supplied with The reaction whichtakes place in the reaction zone converts the sodium sulfide in thesolution to sodium sulfite and the treated solution is passed intoreceiving tank 12. This treated solution is accompanied by steam vapors,and spent air, which will pass into the pipe 59 and thence into coolingchamber 13 which is maintained at cooling temperature by circulation ofcooling water through coil 54. This causes the-steam and entrainedchemical reagent to collect as liquidsolution in the condenser and thecondensed solution gravitates back througi the pipe 59 into thereceiving tank 12. Uncondensed gases and vapors minus all entrained orVolatiiized chemicals pass through vent 57 as waste to atmosphere.The-treated solution 58 in which the sodium sulfide has been convertedto sodium sulfite may be drawn off through pipe ddfor reuse in thedigesters of the pulp plant. 7

The examples set forth in the following Table I' will serve further toillustrate the process of my invention.

' The raw solution was made by dissolving a smelt in water,

the smelt having been produced in. a process of recovering the chemicalsfrom black liquor from the digesters of a pulp plant. The raw solutioncontained the compounds as shown in the table under the columns labelled.Before Treatment. The raw solution together with air in an amount toprovide an. excess of oxygen to convert the sodium sulfide to sodiumsulfite was passed through the reaction zone as described above. Thetemperatures and pressures indicated in the table were maintained in thereaction zone. The results of the treatment are shown in the steamwithinsaid chamber within the range of sixty m 0;) range of 310 F. to 350 F.at which said sodium sulfide isoxidized in an exothermic reaction, tosodium sulfite,

controlling said pressure in said zone at said constant pressure wherebyany excess heat produced by the exothermic oxidation of the sodiumsulfide to sodium sulfite which would cause the'ternperature in saidzone to rise above said given temperature is taken up as latent heat ofvaporization inthe conversion of water 'into'steam, thereby to maintainthe. temperature in said zone substantially constant. I

2. A process for converting sodium sulfide to sodium sulfite whichcomprises passing'a charge containing an' and one hundred twenty-fivepounds per square inch.

3 A process of converting sodium sulfide into sodium sulfite whichcomprises passing a stream of aqueous solution of the sodium sulfide inan atmosphere of saturated steam and air through 'a'reaction chamber,subdividing the stream being treated into thin" surface films-thereby toexpose the sulfide to the oxygen in the auto promote oxidation of thesulfide while maintaining the pressure'in sulfite which comprisespassing an aqueous solution containing sodium sulfide through a reactionzone in an at mosphere of saturated steam and air under substantiallyconstant pressure within therange of 60 to 125 poundspe'r'square inchand at a given temperature within the the columns labelled AfterTreatment. It may be noted said chamber between sixty and one hundredtwenty-five that there is a small amount of evaporation of the waterpounds per square inch gauge and the temperature within in the charge asa result of'the treatment. the range of 3l0 F. to 350 F. and controllingand Table I i 7 Run A Bun B Run Q Run D Pressure in Reaction Zone 80p.s.i. 60 psi. 80 p.s.i. 125 psi. Temperature in Reaction Zone 321 F.300 F. 324 F. 350 F.

Solution, Solution, Solution, Solution,

g.p.1. 1 g.p.l. g.p.l. Percent By Wt.

Compound Before After Before After Before After Before After Treat-Treat- 'Ireat- Treat- Treat- Treat- Treat- Treatment ment merit meni:merit merit ment ment 1 Sodium Sulfide N3JS 28.36 0.2 28.36 3.22. 21.700.5 12.51 .02 Sodium Thiosulfate 2.03 4.0 2.08 7.66 1.10 4.04 .41 .92

NazSzOa. Sodium Sulfite N21280:)" 1.01 32 1.01 14.11 .95 20.52 .10 14.31Sodium Sulfate NazSO4 2. 4. s 2. 55 5.05 a 2. 01 2. 39 1. 02 1.49 SodiumCarbonate 23.90 21.70 13; 99 15:03

N34003- Sodium Hydroxide .13 .24 Trace Trace NaOH.

1 Grams per liter. 2 Percent by weight. g v

It is contemplated that in some instances in practicing maintaining thetemperature in said reaction zone by my method, modified air or similargaseous oxidizing maintaining the steam therein at a constantpressurebeagent might be used, such, for example, atmospheric air tween sixtyand one-hundred twenty-five pounds 5 per to which is added additionaloxygen. It will be undersquare inch. r v

' stood that the term air as used in the annexedclaims 4. A process foroxidizing sodium sulfide. to sodium is intended to include a gaseousoxidizing agent containsulfite which comprises treating an. aqueoussolution coning a substantial portion of oxygen. taining thesodiumsulfide in an atmosphere of saturated The terms and expressionswhich have been employed steam and air in a reaction zone in Whichsaidsodium herein are used as terms of description and not of limitasulfideis oxidized to. sodium sulfite' in an exothermic tion, and there is nointention, in theuse otsuch terms reaction and maintaining apredetermined constant presand expressions, ofexcluding any equivalentsof the tea-I sure in said zone within the range of80 pounds per turesshown and described'or portions thereof, but it is square inch andonehundred twenty-five pounds i per recognized that various modificationsare possible Within square inch and maintaining the temperature in saidzone the scope of the invention claimed. at a predetermined constanttemperature between 310? F.

What is claimed is: v V and 350 F. by controlling the steam pressure 1nsaid 1. A process for converting sodium sulfide to sodium zone sothatany heat generated in said zone as a result of the exothermic oxidizingreaction which is enough to cause the'temperaturein said zone to riseabove said constant temperature is dissipated as latent heat of vaporiZillion whereby said reaction is controlled to avoid OXlda: qu'of theSulfide tosulfate form,

5. A process for converting sodium sulfide to sodium sulfite whichcomprises treating an aqueous solution containing the sodium sulfide inan atmosphere of saturated steam and air in a reaction zone wherein saidsulfide is oxidized in an exothermic reaction, maintaining the pressurein said zone within the range of 80 to 125 pounds per square inch andmaintaining the temperature in said zone at a substantially constanttemperature within the range of 310 F. to 350 F. by controlling thepressure in said zone whereby any heat generated in said zone as aresult of the exothermic oxidizing reaction which is in excess of thatwhich causes the temperature in said zone to rise above said constanttemperature is dissipated as latent heat of vaporization.

6. A process for converting sodium sulfide to sodium sulfite whichcomprises passing an aqueous solution containing sodium sulfide togetherwith air and saturated steam under pressure of at least 60 pounds persquare inch through a reaction chamber While maintaining a giventemperature within the range of 310. F. to 350 F. in said chamber atwhichsaid sodium sulfide is oxidized to sodium sulfite; controlling andmaintaining'a constant pressure in said reaction chamber so that anyexcess heat produced by the oxidation of the sodium sulfide to sodiumsulfite which would cause the temperature in said chamher to rise abovesaid given temperature is taken up as latent heat of vaporization by theconversion of water into steam, and thereby maintaining the temperaturein said chamber substantially constant at said given temperature;passing the treated solution containing the sodium sulfite, steam andair, from said reaction chamber into a collecting chamber, and thenpassing any uncondensed steam with the residual air into a condenserchamber maintained at a temperature to condense the steam to recoverentrained sodium compounds, and then discharging residual uncondensedaqueous vapor and residual air from said condenser chamber,

7. A process for converting sodium sulfide to sodium sulfite whichcomprises passing an aqueous solution containing sodium sulfide togetherwith air and saturated steam under pressure higher than atmosphericpressure through a reaction chamber while maintaining a giventemperature within the range of 310 F. to 350 F. in said chamber atwhich said sodium sulfide is oxidized to sodium sulfite and oxidation tosodium sulfate is avoided; controlling the pressure in said zone at agiven pressure within the range of 80 to 125 pounds per square inch sothat any excess heat produced by the oxidation of the sodium sulfide tosodium sulfite which would cause the temperature in said chamber to riseabove said given temperature is taken up as latent heat of vaporizationby the conversion of water into steam, and thereby maintaining thetemperature in said chamber substantially constant at said giventemperature to avoid formation of sodium sulfate; passing the treatedsolution containing the sodium sulfite, steam and air, from saidreaction chamber into a collecting chamber, and then passing anyuncondensed steam with the residual air into a condenser chambermaintained at a temperature to condense the steam and to recoverentrained sodium compounds, and then discharging residual uncondensedaqueous vapor and residual air from said condenser chamber.

References Cited by the Examiner UNITED STATES PATENTS Ross et a1 23-283X MAURICE A. BRINDISI, Primary Examiner.

1. A PROCESS FOR CONVERTING SODIUM SULFIDE TO SODIUM SULFITE WHICHCOMPRISES PASSING AN AQUEOUS SOLUTION CONTAINING SODIUM SULFIDE THROUGHA REACTION ZONE N AN ATMOSPHERE OF SATURATED STEAM AND AIR UNDERSUBSTANTIALLY CONSTANT PRESSURE WITHIN THE RANGE OF 60 TO 125 POUNDS PERSQUARE INCH AND AT A GIVEN TEMPERATUER WITHIN THE RANGE OF 310*F. TO350*F. AT WHICH SAID SODIUM SULFIDE IS OXIDIZED IN AN EXOTHERMICREACTION, TO SODIUM SULFITE, CONTROLLING SAID PRESSURE IN SAID ZONE ATSAID CONSTANT PRESSURE WHEREBY ANY EXCESS HEAT PRODUCED BY THEEXOTHERMIC OXIDATION OF THE SODIUM SULFIDE TO SODIUM SULFITE WHICH WOULDCAUSE THE TEMPERATURE IN SAID ZONE TO RISE ABOVE SAID GIVEN TEMPERATUREIS TAKEN UP AS LATENT HEAT